Purpose: :
The laws of Stokes-Einstein and Fick postulate that the rateof diffusion is inversely related to the viscosity of the medium.The viscosity of vitreous gel is greater than water. In vitrectomythe vitreous gel is removed and replaced with saline and thediffusion coefficient and the rate of transport by diffusionwithin the vitreous cavity is increased. We test this hypothesisin vitro using O2 as the signal molecule.

Methods: :
Specially designed diffusion cells were used (PermeGear, Inc,Hellertown, PA, USA) with a middle chamber filled with eithersaline solution or porcine vitreous humour, separated by cellophanemembranes (MWCO 12,000-14,000). The decreasing pO2 was measuredin a lower chamber as oxygen diffused through vitreous humouror saline solution to an upper chamber, where pure N2 bubbled.A double layer of cellophane membranes was used as a reference,with no middle chamber. An oxygen sensor, OxyLab pO2 (OxfordOptronix Ltd., Oxford, UK) was used to measure the concentrationof oxygen under standardized conditions. The diffusion coefficientof the vitreous gel and saline solution were calculated, usingFick’s law. The resistance of the membranes was subtractedin order to find the diffusion coefficient for the vitreousgel or saline solution only.